luci-lib-jsonc: Add ltn12-compatible sink factory

To use the luci-lib-jsonc parser as sink for an ltn12 pump (for example
from stdin), the following code will now do:

    require 'luci.ltn12'
    require 'luci.jsonc'

    local parser = luci.jsonc.new()
    luci.ltn12.pump.all(luci.ltn12.source.file(io.input()), parser:sink())
    print(parser:get())

Signed-off-by: Jan-Philipp Litza <janphilipp@litza.de>

documentation/api/modules/luci.jsonc.parser.html

@@ -233,6 +233,13 @@ Convert parsed JSON data into Lua table.</td>
 Put Lua data into the parser.</td>
 	</tr>
 
+	<tr>
+	<td class="name" nowrap><a href="#parser.sink">parser:sink</a>&nbsp;()</td>
+	<td class="summary">
+ 
+Generate an ltn12-compatible sink.</td>
+	</tr>
+
 	<tr>
 	<td class="name" nowrap><a href="#parser.stringify">parser:stringify</a>&nbsp;(pretty)</td>
 	<td class="summary">
@@ -406,6 +413,34 @@ Nothing is returned.
 
 
 
+<dt><a name="parser.sink"></a><strong>parser:sink</strong>&nbsp;()</dt>
+<dd>
+
+ 
+Generate an ltn12-compatible sink. 
+
+
+
+
+
+
+<h3>Usage:</h3>
+<pre>parser = luci.jsonc.new() 
+ltn12.pump.all(ltn12.source.file(io.input()), parser:sink()) 
+print(parser:get())</pre>
+
+
+
+<h3>Return value:</h3>
+Returns a function that can be used as an ltn12 sink.
+
+
+
+</dd>
+
+
+
+
 <dt><a name="parser.stringify"></a><strong>parser:stringify</strong>&nbsp;(pretty)</dt>
 <dd>
 

libs/luci-lib-jsonc/src/jsonc.c

@@ -328,6 +328,76 @@ static int json_parse_set(lua_State *L)
 	return 0;
 }
 
+static int json_parse_sink_closure(lua_State *L)
+{
+	bool finished = lua_toboolean(L, lua_upvalueindex(2));
+	if (lua_isnil(L, 1))
+	{
+		// no more data available
+		if (finished)
+		{
+			// we were finished parsing
+			lua_pushboolean(L, true);
+			return 1;
+		}
+		else
+		{
+			lua_pushnil(L);
+			lua_pushstring(L, "Incomplete JSON data");
+			return 2;
+		}
+	}
+	else
+	{
+		if (finished)
+		{
+			lua_pushnil(L);
+			lua_pushstring(L, "Unexpected data after complete JSON object");
+			return 2;
+		}
+		else
+		{
+			// luci.jsonc.parser.chunk()
+			lua_pushcfunction(L, json_parse_chunk);
+			// parser object from closure
+			lua_pushvalue(L, lua_upvalueindex(1));
+			// chunk
+			lua_pushvalue(L, 1);
+			lua_call(L, 2, 2);
+
+			if (lua_isnil(L, -2))
+			{
+				// an error occurred, leave (nil, errmsg) on the stack and return it
+				return 2;
+			}
+			else if (lua_toboolean(L, -2))
+			{
+				// finished reading, set finished=true and return nil to prevent further input
+				lua_pop(L, 2);
+				lua_pushboolean(L, true);
+				lua_replace(L, lua_upvalueindex(2));
+				lua_pushnil(L);
+				return 1;
+			}
+			else
+			{
+				// not finished reading, return true
+				lua_pop(L, 2);
+				lua_pushboolean(L, true);
+				return 1;
+			}
+		}
+	}
+}
+
+static int json_parse_sink(lua_State *L)
+{
+	luaL_checkudata(L, 1, LUCI_JSONC_PARSER);
+	lua_pushboolean(L, false);
+	lua_pushcclosure(L, json_parse_sink_closure, 2);
+	return 1;
+}
+
 static int json_tostring(lua_State *L)
 {
 	struct json_state *s = luaL_checkudata(L, 1, LUCI_JSONC_PARSER);
@@ -367,6 +437,7 @@ static const luaL_reg jsonc_parser_methods[] = {
 	{ "parse",			json_parse_chunk  },
 	{ "get",			json_parse_get    },
 	{ "set",			json_parse_set    },
+	{ "sink",			json_parse_sink   },
 	{ "stringify",		json_tostring     },
 
 	{ "__gc",			json_gc           },

libs/luci-lib-jsonc/src/jsonc.luadoc

@@ -121,10 +121,22 @@ parser:set({ "some", "data" })`
 ]]
 
 ---[[
-Serialize current parser state as JSON.
+Generate an ltn12-compatible sink.
 
 @class function
 @sort 4
+@name parser.sink
+@return Returns a function that can be used as an ltn12 sink.
+@usage `parser = luci.jsonc.new()
+ltn12.pump.all(ltn12.source.file(io.input()), parser:sink())
+print(parser:get())`
+]]
+
+---[[
+Serialize current parser state as JSON.
+
+@class function
+@sort 5
 @name parser.stringify
 @param pretty A boolean value indicating whether the resulting JSON should be pretty printed.
 @return Returns the serialized JSON data of this parser instance.